1. Field of the Invention
The present invention relates to injection molding in general, and in particular to molding with sacrificial inserts, particularly for ceramic and metals.
2. Description of the Known Art
Injection molding is used to manufacture articles of complex geometry. This method is useful for plastic parts as well as metal and ceramic parts prepared by powder injection molding. Injection molding while being generally economical for large volumes of parts can be uneconomical for short-run or prototype production. Moreover, obtaining certain features such as undercuts and blind holes in certain orientations in an injection molded part is either difficult or impossible, or requires complex and expensive tooling.
There are numerous examples of the use of complex tooling solutions such as expanding cores, see, e.g., Holdred, xe2x80x9cExpandable Core Assembly,xe2x80x9d U.S. Pat. No. 3,731,901; Catalanotti, and Tarahomi, xe2x80x9cInjection molding method and system with expandable cavity element,xe2x80x9d U.S. Pat. No. 5,630,977; Pietrorazio, xe2x80x9cCollapsible core for molding closures having interrupted interior threads and the like,xe2x80x9d U.S. Pat. No. 4,938,679; and Mangone, xe2x80x9cApparatus and method for molding three dimensional articles,xe2x80x9d U.S. Pat. No. 4,956,142, and slides, e.g., Schulz, Kaiser, and Temesvary, xe2x80x9cProcess for injection molding arcuately-shaped hollow articles,xe2x80x9d U.S. Pat. No. 5,433,912; Kaneishi, Kiboshi, Mio, and Fukui, xe2x80x9cMold apparatus and injection molding method for producing hollow-structured article by injection molding,xe2x80x9d U.S. Pat. No. 5,656,234; and Foltuz; and Cohan, xe2x80x9cModular mold for injection molding and method of use thereof,xe2x80x9d U.S. Pat. No. 5,595,771, for the production of otherwise difficult geometry""s of injection molded parts. These tooling solutions allow for the molding of some geometries, but there are limitations to the complexity of parts possible, and the cost of such tools may be prohibitive.
The known art is also replete with examples of the use of expendable patterns in the forming of complex shapes. The casting industry commonly uses xe2x80x9clost wax,xe2x80x9d and xe2x80x9clost foamxe2x80x9d processes. In these processes, a mold is formed around a shaped material of wax, injection molded plastic, or polymeric foam. It is the purpose of this material to form the cavity and be vaporized upon casting of the molten metal. See, e.g., U.S. Pat. No. 5,906,234.
U.S. Pat. Nos. 5,614,232 and 5,242,646 to Torigoe et al. describe methods for making fasteners by injection molding in which a sacrificial stem mold is used for defining exterior contours. U.S. Pat. No. 5,824,250 to Whalen et al. describes gel cast ceramic manufacturing using a fugitive mold. U.S. Pat. Nos. 5,248,552 and 5,089,186 to Moore et al. describe a method for removing a core from a cast molded product, which is an inert particulate material with a water soluble carbohydrate binder. U.S. Pat. No. 5,681,518 to Ashcraft describes an injection molding process in which a plurality of different mold components (including core components) of defined contour are formed and combined.
U.S. Pat. No. 5,176,866 to Tanka and U.S. Pat. No. 5,173,237 to Kidd describe molding cores that use low melting point alloys which may be removed from a molded article by heat, such as hot oil. U.S. Pat. No. 4,614,627 to Curtis et al. describes a method for molding a golf club head which uses a fusible core which can be melted out after the injected material sets. U.S. Pat. No. 5,143,665 to Cubbs et al. describe a sacrificial mold used to mold composite materials, plastic or metals.
There is a need, however, for a molding system which utilizes a sacrificial insert which is capable of forming interior features of an injection molded article, and which is able to maintain fidelity of the features being molded under the conditions of injection molding. There is also a need for a mold combination which can use different combinations of sacrificial parts and permanent parts to provide optimum economy when molding articles, particularly articles having complex geometries which are difficult to mold with conventional molds, such as those described above and short-run or prototype molded objects. There is also a need for a multi-shot process which can economically produce short run parts having complex features not normally attainable with conventional multi-shot molds.
One object of the invention is to overcome the disadvantages of the known art described above. Another object of the invention is to provide a sacrificial insert for injection molding an object, and a mold which includes the sacrificial insert. Yet another object is to provide a method of injection molding an object using a sacrificial insert. Still another object of the invention is to provide a method for producing an object by multi-shot injection molding the object using a sacrificial insert. Yet another object of the invention is to provide a method for forming a molded ceramic object or a molded metal object by injection molding using a sacrificial insert.
In order to achieve the foregoing and further objects, there has been provided according to one aspect of the invention, a sacrificial insert for injection molding an object from a base material, which includes, a water-insoluble insert which has a melting temperature greater than the injection molding melt temperature of the base material. According to another aspect of the invention, there has been provided a mold for making an object by injection molding, which includes, a support base and the sacrificial insert described above, and optionally a tool.
According to yet another aspect of the invention, there has been provided a method of injection molding an object formed of a base material, which includes: providing a mold having the sacrificial insert described; providing the base material in a flowable state; flowing the base material into the mold and into contact with the sacrificial insert; solidifying the base material in the mold to form the molded object; and destructively disengaging the sacrificial insert from the molded object without substantially damaging the molded object.
According to still another aspect of the invention, there has been provided a method of removing a sacrificial insert from a molded object, which includes, subjecting the sacrificial insert described above and the molded object to a treatment sufficient to destroy the sacrificial insert and enable it to be removed from the molded object without substantially damaging the molded object.
According to a further aspect of the invention, there has been provided a mold for making an object by injection molding comprising one or more of: a sacrificial insert configured to form interior features of the object; a sacrificial insert configured to form interior and exterior features of the object; and a combination of a sacrificial insert configured to form exterior features of the object and a tool configured to form interior features of the object.
According to yet another aspect of the invention, there has been provided a method for producing an object comprising, multi-shot injection molding the object which injection molding includes: providing a support base containing a tool; injecting a first material into the support base to form an integral tool and sacrificial insert; separating the tool from the sacrificial insert; retaining the sacrificial insert in the support base, or inserting the sacrificial insert into another support base optionally having a further sacrificial insert or tool; injecting a second material into the support base containing the sacrificial insert to form an integral sacrificial insert and molded object; destructively disengaging the sacrificial insert from the molded object without substantially damaging the molded object.
According to a further aspect of the invention, there has been provided a method for forming a molded ceramic object, which includes: providing a mold having a sacrificial insert; providing a ceramic injection molding feedstock; flowing the ceramic feedstock into the mold and into contact with the sacrificial insert; solidifying the ceramic material in the mold to form an integral green molded ceramic object and sacrificial insert; and subjecting the integral green molded ceramic object and sacrificial insert to a treatment sufficient to destroy the sacrificial insert, whereby the sacrificial insert can be separated from the molded ceramic object without substantially damaging the molded object.
According to a further aspect of the invention, there has been provided a method for forming a molded metal object, which includes: providing a mold having a sacrificial insert; providing a metal injection molding feedstock; flowing the metal feedstock into the mold and into contact with the sacrificial insert; solidifying the metal material in the mold to form an integral green molded metal object and sacrificial insert; and subjecting the integral green molded metal object and sacrificial insert to a treatment sufficient to destroy the sacrificial insert, whereby the sacrificial insert can be separated from the molded metal object without substantially damaging the molded object.
Further objects, features and advantages of the present invention, will become readily apparent from detailed consideration of the preferred embodiments which follow.